Re: [PATCH 2/8] LoongArch: Only use -Wa,-mla-* options for !CONFIG_CC_HAS_EXPLICIT_RELOCS

From: Huacai Chen
Date: Sun Aug 28 2022 - 10:16:10 EST


Hi, Ruoyao,

On Sun, Aug 28, 2022 at 1:55 AM Xi Ruoyao <xry111@xxxxxxxxxxx> wrote:
>
> If explicit relocation hints is used by the toolchain, -Wa,-mla-*
> options will be useless for C code. Only use them for
> !CONFIG_CC_HAS_EXPLICIT_RELOCS.
>
> Replace "la" with "la.pcrel" in head.S to keep the semantic consistent
> with new and old toolchains for the low level startup code.
>
> Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxx>
> ---
> arch/loongarch/Makefile | 15 ++++++++++++++-
> arch/loongarch/kernel/head.S | 10 +++++-----
> 2 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 415e09bdf31a..bd0ea6623245 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -40,10 +40,23 @@ endif
>
> cflags-y += -G0 -pipe -msoft-float
> LDFLAGS_vmlinux += -G0 -static -n -nostdlib
> +
> +ifdef CONFIG_CC_HAS_EXPLICIT_RELOCS
> +# GCC may have -mexplicit-relocs off by default if it was built with an old
> +# assembler. But with CONFIG_CC_HAS_EXPLICIT_RELOCS we are sure explicit
> +# relocation hints are supported by the assembler, so force it.
> +cflags-y += -mexplicit-relocs
> +else
> +# Likewise, disable -mexplicit-relocs if GCC enables by default but the
> +# assembler does not support it.
> +cflags-y += $(call cc-option,-mno-explicit-relocs)
> +# With -mno-explicit-relocs, use assembler options to adjust code generation
> +# for symbol address.
> KBUILD_AFLAGS_KERNEL += -Wa,-mla-global-with-pcrel
> KBUILD_CFLAGS_KERNEL += -Wa,-mla-global-with-pcrel
> KBUILD_AFLAGS_MODULE += -Wa,-mla-global-with-abs
> -KBUILD_CFLAGS_MODULE += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs
> +KBUILD_CFLAGS_MODULE += -Wa,-mla-global-with-abs,-mla-local-with-abs
> +endif
Move all comments out of #ifdefs may make code more clear.


Huacai
>
> cflags-y += -ffreestanding
> cflags-y += $(call cc-option, -mno-check-zero-division)
> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
> index 01bac62a6442..eb3f641d5915 100644
> --- a/arch/loongarch/kernel/head.S
> +++ b/arch/loongarch/kernel/head.S
> @@ -55,17 +55,17 @@ SYM_CODE_START(kernel_entry) # kernel entry point
> li.w t0, 0x00 # FPE=0, SXE=0, ASXE=0, BTE=0
> csrwr t0, LOONGARCH_CSR_EUEN
>
> - la t0, __bss_start # clear .bss
> + la.pcrel t0, __bss_start # clear .bss
> st.d zero, t0, 0
> - la t1, __bss_stop - LONGSIZE
> + la.pcrel t1, __bss_stop - LONGSIZE
> 1:
> addi.d t0, t0, LONGSIZE
> st.d zero, t0, 0
> bne t0, t1, 1b
>
> - la t0, fw_arg0
> + la.pcrel t0, fw_arg0
> st.d a0, t0, 0 # firmware arguments
> - la t0, fw_arg1
> + la.pcrel t0, fw_arg1
> st.d a1, t0, 0
>
> /* KSave3 used for percpu base, initialized as 0 */
> @@ -73,7 +73,7 @@ SYM_CODE_START(kernel_entry) # kernel entry point
> /* GPR21 used for percpu base (runtime), initialized as 0 */
> move u0, zero
>
> - la tp, init_thread_union
> + la.pcrel tp, init_thread_union
> /* Set the SP after an empty pt_regs. */
> PTR_LI sp, (_THREAD_SIZE - 32 - PT_SIZE)
> PTR_ADD sp, sp, tp
> --
> 2.37.0
>